SPI library usage in Arduino - Mini Project: Build & Apply

SPI Library Usage in Arduino

📖 Scenario: You are building a simple Arduino project that communicates with an SPI device, like a sensor or display. SPI (Serial Peripheral Interface) is a way for your Arduino to talk to other devices quickly using a few wires.In this project, you will learn how to set up SPI communication using the Arduino SPI library, send data to the SPI device, and read data back.

🎯 Goal: Build a simple Arduino program that initializes SPI communication, sends a byte of data to an SPI device, and reads a byte back.

📋 What You'll Learn

Use the Arduino SPI library

Initialize SPI communication with SPI.begin()

Set SPI settings with SPISettings

Send data using SPI.transfer()

Read data returned from SPI.transfer()

Use a chip select pin to control the SPI device

💡 Why This Matters

🌍 Real World

SPI is used in many electronics projects to connect microcontrollers to sensors, displays, memory chips, and other devices quickly and efficiently.

💼 Career

Understanding SPI communication is important for embedded systems engineers, hardware developers, and anyone working with microcontrollers and electronics.

1

Setup SPI and Chip Select Pin

Create a variable called chipSelectPin and set it to 10. In the setup() function, set chipSelectPin as an output and set it HIGH. Then call SPI.begin() to start SPI communication.

Arduino

int chipSelectPin = 10;

void setup() {
  pinMode(chipSelectPin, OUTPUT);
  digitalWrite(chipSelectPin, HIGH);
  SPI.begin();
  // Your code here
}

void loop() {
  // Your code here
}

Hint

Remember to set the chip select pin as output and set it HIGH before starting SPI.

2

Configure SPI Settings

Create a variable called spiSettings using SPISettings with a clock speed of 4000000 (4 MHz), data order MSBFIRST, and SPI mode SPI_MODE0.

Arduino

int chipSelectPin = 10;

SPISettings spiSettings(4000000, MSBFIRST, SPI_MODE0);

void setup() {
  pinMode(chipSelectPin, OUTPUT);
  digitalWrite(chipSelectPin, HIGH);
  SPI.begin();
  // Your code here
}

void loop() {
  // Your code here
}

Hint

Use SPISettings with the exact parameters: 4000000, MSBFIRST, SPI_MODE0.

3

Send and Receive Data Using SPI.transfer()

In the loop() function, use SPI.beginTransaction(spiSettings) to start SPI communication. Then set chipSelectPin LOW to select the device. Send the byte 0x42 using SPI.transfer() and store the returned byte in a variable called receivedData. Set chipSelectPin HIGH to deselect the device. Finally, call SPI.endTransaction().

Arduino

int chipSelectPin = 10;

SPISettings spiSettings(4000000, MSBFIRST, SPI_MODE0);

void setup() {
  pinMode(chipSelectPin, OUTPUT);
  digitalWrite(chipSelectPin, HIGH);
  SPI.begin();
}

void loop() {
  SPI.beginTransaction(spiSettings);
  digitalWrite(chipSelectPin, LOW);
  byte receivedData = SPI.transfer(0x42);
  digitalWrite(chipSelectPin, HIGH);
  SPI.endTransaction();
  // Your code here
}

Hint

Use SPI.beginTransaction and SPI.endTransaction around your SPI transfer. Remember to control the chip select pin.

4

Print the Received Data

Add Serial.begin(9600) in the setup() function to start serial communication. In the loop() function, after receiving data, print the text "Received: " followed by the value of receivedData using Serial.println(). Add a delay of 1000 milliseconds at the end of loop().

Arduino

int chipSelectPin = 10;

SPISettings spiSettings(4000000, MSBFIRST, SPI_MODE0);

void setup() {
  pinMode(chipSelectPin, OUTPUT);
  digitalWrite(chipSelectPin, HIGH);
  SPI.begin();
  Serial.begin(9600);
  // Your code here
}

void loop() {
  SPI.beginTransaction(spiSettings);
  digitalWrite(chipSelectPin, LOW);
  byte receivedData = SPI.transfer(0x42);
  digitalWrite(chipSelectPin, HIGH);
  SPI.endTransaction();
  Serial.print("Received: ");
  Serial.println(receivedData);
  delay(1000);
  // Your code here
}

Hint

Use Serial.begin(9600) in setup() and print the received data with Serial.print and Serial.println.

Practice

1. What is the main purpose of the SPI.begin() function in Arduino's SPI library?

easy

A. To close the SPI communication

B. To initialize the SPI bus and prepare it for communication

C. To set the SPI clock speed

D. To send a byte of data over SPI

Solution

1. Step 1: Understand the role of SPI.begin()

   The SPI.begin() function sets up the SPI hardware and pins for communication.

2. Step 2: Differentiate from other SPI functions

   Functions like SPI.transfer() send data, while SPI.beginTransaction() sets speed and mode, but SPI.begin() only initializes.

3. Final Answer:

   To initialize the SPI bus and prepare it for communication -> Option B

4. Quick Check:

   SPI.begin() initializes SPI [OK]

Hint: Remember: begin() always starts or initializes [OK]

Common Mistakes:

• Confusing SPI.begin() with SPI.transfer()
• Thinking SPI.begin() sets speed or mode
• Assuming SPI.begin() closes communication

2. Which of the following is the correct syntax to send a byte of data using the SPI library in Arduino?

easy

A. SPI.send(0xFF);

B. SPI.sendByte(0xFF);

C. SPI.write(0xFF);

D. SPI.transfer(0xFF);

Solution

1. Step 1: Identify the correct SPI function for sending data

   The Arduino SPI library uses SPI.transfer() to send and receive a byte simultaneously.

2. Step 2: Check syntax correctness

   Only SPI.transfer(0xFF); matches the correct function and parameter format.

3. Final Answer:

   SPI.transfer(0xFF); -> Option D

4. Quick Check:

   SPI.transfer() sends data byte [OK]

Hint: Use transfer() to send and receive SPI bytes [OK]

Common Mistakes:

• Using non-existent functions like send() or sendByte()
• Confusing SPI.transfer() with SPI.begin()
• Using write() which is not part of SPI library

3. What will be the output of this Arduino code snippet using SPI?

SPI.begin();
byte response = SPI.transfer(0xAA);
Serial.println(response, HEX);

Assuming the SPI slave device echoes back the sent byte.

medium

A. AA

B. 55

C. 00

D. FF

Solution

1. Step 1: Understand SPI.transfer() behavior

   The SPI.transfer() sends a byte and simultaneously receives a byte from the slave device.

2. Step 2: Analyze the slave device response

   The slave echoes back the sent byte 0xAA, so response will be 0xAA.

3. Final Answer:

   AA -> Option A

4. Quick Check:

   Sent byte echoed back = AA [OK]

Hint: SPI.transfer() returns the received byte immediately [OK]

Common Mistakes:

• Assuming transfer() only sends without receiving
• Expecting a different response byte
• Confusing HEX output with decimal

4. Identify the error in this Arduino SPI code snippet:

SPI.beginTransaction(SPISettings(4000000, MSBFIRST, SPI_MODE0));
SPI.transfer(0x01);
SPI.endTransaction();
SPI.begin();

medium

A. SPI.begin() should be called before SPI.beginTransaction()

B. SPI.endTransaction() is missing

C. SPI.transfer() cannot be used inside a transaction

D. SPISettings parameters are incorrect

Solution

1. Step 1: Check SPI initialization order

   SPI.begin() must be called once before starting any transaction to initialize SPI hardware.

2. Step 2: Verify transaction usage

   The code calls SPI.beginTransaction() before SPI.begin(), which is incorrect and causes errors.

3. Final Answer:

   SPI.begin() should be called before SPI.beginTransaction() -> Option A

4. Quick Check:

   Initialize SPI first with begin() [OK]

Hint: Always call SPI.begin() before transactions [OK]

Common Mistakes:

• Calling beginTransaction() before begin()
• Forgetting to call endTransaction()
• Misunderstanding SPISettings parameters

5. You want to communicate with two SPI devices on the same Arduino. How should you manage SPI transactions to avoid conflicts?

hard

A. Use SPI.transfer() without transactions for both devices

B. Call SPI.begin() twice, once for each device

C. Call SPI.beginTransaction() with each device's settings before communication and SPI.endTransaction() after

D. Connect both devices to the same chip select pin

Solution

1. Step 1: Understand SPI multi-device communication

   Each SPI device may require different speed or mode settings, so transactions help manage these safely.

2. Step 2: Use transactions properly

   Call SPI.beginTransaction() with the device's settings before communicating, then SPI.endTransaction() after to avoid conflicts.

3. Final Answer:

   Call SPI.beginTransaction() with each device's settings before communication and SPI.endTransaction() after -> Option C

4. Quick Check:

   Use transactions per device to avoid conflicts [OK]

Hint: Use beginTransaction/endTransaction per device [OK]

Common Mistakes:

• Calling SPI.begin() multiple times
• Sharing chip select pins for different devices
• Skipping transactions causing wrong settings